In the human body, increased metabolic activity is associated with an increase in emitted radiation. In the field of nuclear medicine, increased metabolic activity within a patient is detected using a radiation detector such as a scintillation camera.
Scintillation cameras are well known in the art, and are used for medical diagnostics. A patient ingests, or inhales or is injected with a small quantity of a radioactive isotope. The radioactive isotope emits photons that are detected by a scintillation medium in the scintillation camera. The scintillation medium is commonly a sodium iodide crystal, BGO or other. The scintillation medium emits a small flash or scintillation of light, in response to stimulating radiation, such as from a patient. The intensity of the scintillation of light is proportional to the energy of the stimulating photon, such as a gamma photon. Note that the relationship between the intensity of the scintillation of light and the gamma photon is not entirely linear.
A conventional scintillation camera such as a gamma camera includes a detector which converts into electrical signals gamma rays emitted from a patient after radioisotope has been administered to the patient. The detector includes a scintillator and photomultiplier tubes. The gamma rays are directed to the scintillator which absorbs the radiation and produces, in response, a very small flash of light. An array of photodetectors, which are placed in optical communication with the scintillation crystal, converts these flashes into electrical signals which are subsequently processed. The processing enables the camera to produce an image of the distribution of the radioisotope within the patient.
Gamma radiation is emitted in all directions and it is necessary to collimate the radiation before the radiation impinges on the crystal scintillator. This is accomplished by a collimator which is a sheet of absorbing material, usually lead, perforated by relatively narrow channels. The collimator is detachably secured to the detector head, allowing the collimator to be changed to enable the detector head to be used with the different energies of isotope to suit particular characteristics of the patient study. A collimator may vary considerably in weight to match the isotope or study type.
Scintillation cameras are used to take four basic types of pictures: spot views, whole body views, partial whole body views, SPECT views, and whole body SPECT views.
A spot view is an image of a part of a patient. The area of the spot view is less than or equal to the size of the field of view of the gamma camera. In order to be able to achieve a full range of spot views, a gamma camera must be positionable at any location relative to a patient.
One type of whole body view is a series of spot views fitted together such that the whole body of the patient may be viewed at one time. Another type of whole body view is a continuous scan of the whole body of the patient. A partial whole body view is simply a whole body view that covers only part of the body of the patient. In order to be able to achieve a whole body view, a gamma camera must be positionable at any location relative to a patient in an automated sequence of views.
The acronym "SPECT" stands for single photon emission computerized tomography. A SPECT view is a series of slice-like images of the patient. The slice-like images are often, but not necessarily, transversely oriented with respect to the patient. Each slice-like image is made up of multiple views taken at different angles around the patient, the data from the various views being combined to form the slice-like image. In order to be able to achieve a SPECT view, a scintillation camera must be rotatable around a patient, with the direction of the detector head of the scintillation camera pointing in a series of known and precise directions such that reprojection of the data can be accurately undertaken.
A whole body SPECT view is a series of parallel slice-like images of a patient. Typically, a whole body SPECT view consists of equally spaced cross sections or vertical or horizontal longitudinal sections. A whole body SPECT view results from the simultaneous generation of whole body and SPECT image data. In order to be able to achieve a whole body SPECT view, a scintillation camera must be rotatable around a patient, with the direction of the detector head of the scintillation camera pointing in a series of known and precise directions such that reprojection of the data can be accurately undertaken.
Therefore, in order that the radiation detector be capable of achieving the above four basic views, the support structure for the radiation detector must be capable of positioning the radiation detector in any position relative to the patient. Furthermore, the support structure must be capable of moving the radiation detector relative to the patient in a controlled manner along any path.
In prior scintillation cameras, the vertical travel of a detector has been achieved by either counter-balancing the detector about a pivot or by a motor driven screw jack. This results in compromises in various areas of normal clinical operation including the possibility of varying the total weight of the detector, raising or lowering the detector and maintaining the focus of the collimator at the same point, the ability to perform complex motions around the patient and view the constant `slice` of the patient and the precision and reproducibility of the motions.
While such scintillation camera systems have existed for about two decades now, performing to a greater or lesser degree satisfactorily, the advances in resolution in newer systems have created greater requirements in precision alignment between the detector and the patient or the patient support apparatus. One alternative system attempted to address this problem at the cost of great complexity. This has been particularly noticeable as nuclear camera systems have been used more and more for generating tomographic images by rotation of the detector about the patient, in addition to the more conventional static imaging. One such nuclear camera system capable of both whole body static imaging as well as emission computed tomography or ECT, is the Gemini system available from General Electric Corporation, Milwaukee, Wis., and described in U.S. Pat. No. 4,651,007 to Perusek et al.
In general, prior nuclear camera systems, regardless of whether they include ECT capability, feature a counter-balanced detector, with an inherent variable viewing point in the patient due to the radius from the pivot to the detector, a toe or forward projecting structure to stabilize the medical diagnostic positioner or the patient bed supported between two supports with the detector head mounted on a translatable support to traverse the patient length. The loss of resolution and contrast of the imaging device, the scintillation camera detector head, arises from variable viewing point in the patient due to the radius from the pivot to the detector and from a lack of precision alignment between the bed and detector head, particularly during rotation of the camera head.
Among the objects of the present invention are to provide: an improved support structure for medical diagnostic equipment, such as a nuclear camera; a support structure capable of supporting and positioning a nuclear camera in any position relative to a patient; a support structure capable of positioning a nuclear camera for spot views, whole body views, SPECT views, and whole body SPECT views; a support structure for a nuclear camera capable of accommodating a range of collimator weights; a support structure for a nuclear camera that is relatively inexpensive to manufacture.